Sunday, November 9, 2014

The storm system around the November 25-29/Thanksgiving timeframe continues to look like a significant storm system.

OPC

On the morning of November 8th, we saw the remnants of Typhoon Nuri reach peak strength via Ocean Prediction Center observation. As the chart shows here, the massive storm bottomed out at 924 millibars. This means the storm, located at about 170E and 55N, didn't break the record for strongest extratropical cyclone on record, but it certainly came close.

NWS

The graphic above, produced by the National Weather Service in Alaska, shows the observed mean sea level pressure of the storm at that 924mb reading, while the NWS office measured it at 930mb on the chart on the left, where strongest extratropical cyclones in the North Pacific are depicted. For multiple reasons, including the possibility that past storms may have been stronger than that 924mb reading, this storm was not declared the strongest on record in the North Pacific. Despite this, it's quite clear this storm was a historically-strong one, relative to storms in the last 60 or so years.

NOAA

Purely for comparison purposes, the team at KOPN Weather identified a strong storm in the Bering Sea on April 7th, 2011, bottoming out at 936mb, that was about 10 degrees W of where this very strong storm was observed yesterday in the Bering Sea. If you recall what happened about 2-3 weeks after the date of April 7th, we saw a certain tornado outbreak strike the South US, devastating thousands across the country, and causing millions on millions of dollars of damage. If we look at where the resultant storm ended up in mid-late April, utilizing the Bering Sea Rule, we find the storm situated in the Ohio Valley.

WPC

Now, keeping in mind that this sort of correlation is a tough one to use at best, not to mention all the caveats associated with long range forecasting, we could theoretically juxtapose the remnants of Typhoon Nuri and this storm in the Bering Sea on April 7th to get an idea of where the consequential storm in the US may end up. Recalling that the storm in 2011 in the Bering Sea was at about 180 degrees longitude, and almost the exact same latitude as the one observed in the last day or two, we find the remnants of Nuri placed about 10 degrees west of that 2011 storm. If we take the location of that storm system in late April (pictured above) and move it west, like the remnants of Nuri were west of that 2011 Bering Sea storm, we end up with a map like this:

WPC

Continuing this correlation, just to see what would happen, we notice that the remnants of Typhoon Nuri are moving eastward (a bit northeast in the process) in the Bering Sea right now, slowly at that. If this storm somehow does end up in that potential location outlined above, and if enough cold air is available (this will be discussed later), a significant winter weather event may strike the Central Plains, Midwest, Great Lakes, and Ohio Valley. Similarly, if the correlation works out, a severe weather event may strike the South US. Again, many caveats are associated with this method, and this should not be taken as "gospel", or at face value.

Tropical Tidbits

The above image shows temperature anomalies at the 850 millibar level (about 5,000 feet off the ground) over North America, as forecasted by the ECMWF ensembles ten days from today. In this image, we see a large swath of warmer than normal temperatures in the Bering Sea, with colder than normal conditions encompassing much of the United States and southern Canada. This looks to be a persistent pattern in coming days and weeks, as a large block of high pressure looks to set up shop directly over the Arctic, providing for a very cold period for North America. Extrapolating this to Thanksgiving, enough cold air should be in place for at least a modest threat of a significant snow event. Again, bear in mind long range caveats, but such a prognosis is favored right now.

To summarize:

- A potentially significant storm system still looks to evolve in the United States around Thanksgiving.
- Severe weather will be a possibility, namely in the South US.
- Significant snow will be a possibility, predominantly in the Central Plains, Midwest, Ohio Valley, and Great Lakes (for now).
- Thanksgiving travel may be severely hampered by this storm, if it does come to fruition as currently projected.

This is the Final Update for this significant November 8-12 snowstorm.

NWS

Winter storm watches (dark blue) and warnings (pink) have been hoisted across a swath of the Upper Midwest into the Northern Plains, as a strong storm system looks to push south into the US and create a potentially dangerous environment for those caught by surprise from this storm. Winter weather advisories (purple) have also been issued for areas where the storm will strike earlier, compared to those in the Midwest.

Tropical Tidbits

The image above shows the GFS model's forecasted total snowfall from this storm over the next 4 days. We can see how the storm is forecasted to lay down amounts near 12" in the Northern Plains, before unleashing on the Upper Midwest. The yellow swath shows amounts in excess of 18" of snow, while those brown-ish areas depict amounts close to two feet of snow. Going by this forecast, we would see the brunt of the storm strike central and northern Wisconsin, as well as the Upper Peninsula of Michigan. Significant amounts would still impact portions of Minnesota and the Dakotas, but Wisconsin would receive the heaviest totals.

Tropical Tidbits

We'll next look over the forecast from the GFS-Parallel model, the newer version of the GFS model which will replace the current model in coming months. This GFS-Parallel model is rumored to be more accurate in multiple aspects of its forecasts, and this storm looks to be its first real test. The GFS-Parallel shifts the bulk of the snow east, now slamming the Upper Peninsula of Michigan into south-central Canada with those two-foot totals. Amounts in Wisconsin would still near 24", but not as widespread as the current GFS model shows. Minnesota is also forecasted here to receive heavier snow, extending into the Dakotas as well.

Regardless of which model you're looking at, the picture is clear: this storm will bring very heavy, very early-season snow to the Upper Midwest and North Plains.

WPC

The Weather Prediction Center issues probabilistic forecasts for snowfall amounts in a given period. In the above image, we see the WPC's forecast for the likelihood of 12" of snow falling in a 24 hour period, centered around November 11th. The WPC places the likelihood at around 50%, a value that's likely to rise as we get closer to the storm's impact and confidence increases.

To summarize:

- A significant winter storm is forecasted to affect the North Plains and Upper Midwest.
- Amounts nearing 24" may be expected, especially in Wisconsin and the Upper Peninsula of Michigan.
- Preparations for this storm should begin now.

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